The present invention relates to mobile communications, and more particularly to methods and apparatuses for operating a mobile device to avoid or alleviate overload conditions in a mobile communication system.
The forthcoming Evolved-Universal Terrestrial Radio Access Network (E-UTRAN) Long Term Evolution (LTE) technology, as defined by 3GPP TR 36.201, “Evolved Universal Terrestrial Radio Access (E-UTRA); Long Term Evolution (LTE) physical layer; General description” will be able to operate over a very wide span of operating bandwidths (e.g., 1.4 MHz to 20 MHz) and also carrier frequencies. Furthermore E-UTRAN systems will be capable of operating within a large range of distances, from microcells (i.e., cells served by low power base stations that cover a limited area, such as a shopping center or other building accessible to the public) up to macrocells having a range that extends up to 100 km. In order to handle the different radio conditions that may occur in the different applications, multiple access in the downlink (i.e., the communications link from the base station to user equipment—“UE”) is achieved by Orthogonal Frequency Division Multiple Access (OFDMA) technology because it is a radio access technology that can adapt very well to different propagation conditions. In OFDMA, the available data stream is portioned out into a number of narrowband subcarriers that are transmitted in parallel. Because each subcarrier is narrowband it only experiences flat-fading. This makes it very easy to demodulate each subcarrier at the receiver.
Data rates over 300 Mb/s will be supported for the largest bandwidth, and such data rates will be possible by using a Multiple-Input-Multiple Output (MIMO) scheme in the down-link.
The possibility of higher data rates in combination with other requirements for more and more functionality within smaller and smaller mobile devices increases the likelihood of high power consumption in those devices and this, in turn, makes the possibility of severe heating problems ever more likely. Heating increases the risk for damage of the circuits in the mobile device. Thus, there is a need to reduce the risk of overheating a mobile device.
Even if a circuit has not yet reached damaging levels of temperature, its correct operation is jeopardized as it approaches such temperatures. The temperature level at which this happens depends on the circuit and bus clocking speed and battery voltage. Hence, there is an intricate dependency between allowable temperature, battery voltage, and clock speeds.
There are other problems associated with the higher data rates in modern mobile communication systems. The high peak data rates allow a system to exploit system capacity gains by appropriate scheduling of the different users. This means there will be a large difference between peak and average data rates for individual users. In some cases, this can lead to an inability of the user equipment to process and buffer all data received in the downlink (i.e., the communication link in the direction from a serving base station to the user equipment).
As to the problem of user equipment being unable to handle a peak downlink data rate, conventional solutions involve scheduling only limited peak data rates to the user equipment. Alternatively, systems may rely entirely on data retransmissions in those instances in which the user equipment was not able to process all received data (e.g., in case of buffer overflow, exceeding signal processing power, or other factors limiting the capability of the user equipment to process instantaneous data rates). But relying on retransmissions after an overload has occurred can give rise to loss of timing in the user equipment's real time processes, which in turn creates a risk of the user equipment going out-of-synchronization and dropping an existing call.
Accordingly, there are a number of user equipment overload conditions (e.g., temperature overload, buffer overflow, signal processing power overload) associated with the higher data rates of modern mobile communications systems. It is therefore desirable to provide methods and apparatuses that handle these problems.